The present invention refers to a pressure medium operated power wrench for turning screws, nuts and the like.
A power wrench is known from U.S. Pat. No. 4,201,099 which has a rotatable ring member within a housing, the ring member being adapted to be connected with the screw head to be turned so as to be rotatable therewith. The ring member is rotated intermittently by a ratchet dog that is reciprocated by a piston movable within a cylinder. A piston rod is connected to the piston by a joint situated within the piston and its other end is connected through a joint to the ratchet dog. By this pendulous mounting of the piston rod, the same is apt to adapt to the different pivotal positions of the ratchet dog relative to the axis of the ring member. The piston has a cylindrical circumferential surface with two sealing rings placed in sealing grooves so that the axis of the piston always coincides with the cylinder axis. It is a drawback of this structure that mounting the piston rod to the piston by joints requires a considerable technical effort and several parts that have to be made separately and assembled thereafter. The individual parts, like the sphere of the joint, the ball cup or the clamping ring of the ball are technically difficult to manufacture with the required high precision.